Electron discharge amplifier



NOV. 23, 1943. w FYLER ELECTRON DISCHARGE AMPLIFIER Filed June 22, 1942Inventor. George W: Fyler, by

JMMI His/Attorney Patented Nov. 23} 1943 2,335,050 ELECTRON DISCHARGEAMPLIFiER George W. Fyler, Stratford, Conn., assignor to GeneralElectric Company, a corporation of New York Application June 22, 1942,Serial No. 447,939

6 Claims. (Cl. 179-171) My invention relates to electron dischargeamplifiers and particularly to such amplifiers operating at frequenciesat which difiiculties are encountered due to low input resistance of thedischarge device.

In amplifiers operating at very high frequencies undesirably lowresistance between the control eelctrode and cathode may result byreason of degeneration produced by the oscillatory currents in theoutput of the discharge device flowing through the unavoidableinductance of the conductor which extends between the cathode of thedischarge device and ground. This conductor may be made as short as itis practical to make it but still has some unavoidable length, andtherefore some inductance, which is common to the output and inputcircuits of the discharge device. The voltage on this inductance ispresent between the control electrode and cathode of the dischargedevice and operates to reduce the resistance between the controlelectrode and cathode. This reduction in resistance may occur to such anextent as to damp to a very objectionable degree the input tuned circuitand thus reduce the sensitivity of the amplifier.

An object of my invention is to reduce the degeneration produced byoscillatory currents of the output circuit of the amplifier flowing inthis common lead to the cathode. v

A further object of my invention is to provide means to maintain thecathode of an electron discharge device operating at such frequencies atground potential.

Another object of my invention is to provide means to produceneutralization of the voltage on this cathode lead.

The novel features which I believe to be characteristic of my inventionare set forth with particularity in the appended claims. My inventionitself, however, both as to its organization and method of operation,together withfurther objects and advantages thereof, may best beunderstoodby'reference to the following description 1 taken inconnection with the accompanying drawing in which Fig. 1 represents anembodiment of my invention and Fig. 2 represents schematically a portionof the circuits of Fig. 1.

Referring to Fig. 1 of the drawing I have shown therein an amplifier Ihaving a cathode 2, a control electrode 3, a screen electrode 4,asuppressor electrode 5 and an anode 6. Between the control electrode 3and cathode 2 is connected a tuned circuit 1, which I have indicated asbeing coupled to a receiving antenna 8, although, of course, any desiredmeans may be employed for exciting in this circuit 1 oscillatoryelectromotive forces to be amplified by amplifier I. These oscillatoryelectromotive forces are amplified by the discharge device I and may besupplied through a coupling condenser 9 to the control grid of asubsequent amplifier I0, if desired. The anode 6 of the discharge deviceis supplied with operating potential from a source of anode voltage thepositive terminal of which is indicated at H and the negative terminal01 which may be grounded as at l2. This circuit may include a suitableresistance l3, high frequency choke coil l4 and tuning inductance IS.The inductance l5 may be proportioned to resonate with such capacity asexists between the anode and cathode of the discharge device I plus thecapacity across the tending within the discharge device.

input of discharge device !0. This latter capacity is indicated indotted lines at IS.

The cathode of the discharge device I is connected to ground through alead conductor having unavoidable inductance, although this conductormay be made as short' as conditions of practice permit. This inductanceis represented at I! and I8. A substantial portion of this inductancemay be that comprised by the lead ex- Oscillatory electromotive forceproduced on these inductances I1 and I8 exists between the controlelectrode 3 and cathode 2 and hence reduces the resistance of thedischarge device for reasons that are well understood in the art.

In accordance with myinvention, means are provided whereby thiselectromotive force is neutralized so that the cathode 2 of thedischarge device I is maintained at ground potential and thus theundesired effects of this voltage are obviated. This result isaccomplished by connecting the lower terminal of anode tuning inductancel5 through'condenser 20 to a point on the cathode lead dividing theinductance of the cathode lead into the two portions l1 and I8. Thiscapacity 20 may be one of'very high value such' that its impedance isentirely negligible at the frequencies involved. If the inductances I1and I8 be proportioned with respect to each other so thatkinductance llbears the same ratio to inductance l8 that the capacity l6 bears to thecapacity 2|, then zero voltage exists between the cathode 2 and groundl2. This capacitance 2| is represented in dottedlines in Fig. 1 andcomprises such capacity as exists between the anode and cathode ofdevice I.

This character of the circuit is better portrayed in Fig. 2 in which thereference characters employed' in Fig. 1 are applied to correspondingelements. The inductance I is shown as having one terminal connected tothe anode of the discharge device I and its lower terminal connected tothe point on the cathode lead between inductances I1 and I8. The inputcapacitance of discharge device II) is indicated at I6 and the totalcapacitance between the anode and cathode of the discharge device I isindicated at 2I. Since inductance I5 resonates with capacitances 2I andI 6, the current may be considered as flowing downward through theinductance I5 and then dividing and flowing in opposite directionsthrough inductances I1 and I8 and hence upward through condensers I6 and2|. Thus, if inductances IT and I8 have a ratio to each other which isthe inverse of that between capacitances 2I and I6, then zero voltageexists between the cathode 2 of discharge device I and ground I2.

Such proportioning of the circuit is highly desirable since it avoidsthe degeneration and reduced input resistance of discharge device Ipreviously referred to and thus avoids the undesired damping of theoscillatory circuit 1, 8 of Fig. 1. This permits sharper tuning of thiscircuit and greater sensitivity of the apparatus.

Of course, if the tuning of the anode circuit of discharge device I bevaried by varying either capacitance I6 or 2I a. certain amount ofregeneration or degeneration will be produced by reason of unequalvoltages on inductances I1 and I8 and a certain amount of damping of thecircuit 1, 8 results. However, no such damping, regeneration, ordegeneration results from variation of tuning by varying inductance I5over a considerable range.

The screen grid 4 of the discharge device I of Fig. 1 is shown assupplied with operating potential from the terminal through a resistance22 and an inductance 23 and as being connected directly to cathode 2through a large bypass condenser 24. Likewise, the suppressor grid 5 isshown connected directly to the cathode 2 of the discharge device. Theseconnections are conventional in amplifiers operating at such frequency,but it is desirable that the capacitance 24 be reasonably large toprevent oscillatory voltages from appearing on the screen grid 4.

If degeneration, or regeneration results to any appreciable extent fromthe fact that the lead to the screen grid 4, or those to condenser 24,have finite length, and therefore finite inductance, such regenerationor degeneration can be compensated for by appropriate change in relativevalues of inductances I1 and I8. Actually this change may be made bysliding the connection of condenser 20 to the cathode lead along thecathode lead until such compensation obtains.

While I have shown a particular embodiment of my invention, it will, ofcourse, be understoodthat I do not wish to be limited thereto sincevarious modifications in the circuit illustrated and instrumentalitiesemployed may be made, and I contemplate by the appended claims to coverany such modifications as fall within the true spirit and scope of myinvention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. In combination, an electron discharge device having an anode andcathode, a capacitive load connected between said anode and cathodethrough an inductance and a second inductance connected between saidanode and an interme- 5 diate point on said first inductance, said pointcathode is at ground potential at the operating frequency. I

3. In combination, an electron discharge device having an anode, and acathode, a capacitive load contacted between said anode and ground, aninductance between said cathode and ground and an inductance betweensaid anode and a point dividing said first inductance into two partshaving a ratio therebetween equal to the ratio of the capacity betweensaid anode and cathode to the capacitance of said load.

4. In combination, a pair of electron discharge devices connected incascade, one of said devices having a cathode; and output electrode andth other having a cathode and input electrode, the latter of saidcathodes being grounded, an inductance between said cathodes, and asecond inductance having one terminal connected to said input and outputelectrodes and its other termi- 35 nal connected to a point'on saidfirst inductance such that said first cathode is maintained at groundpotential atthe operating frequency.

5. The combination, in an electron discharge radio frequency amplifierhaving a control electrode, a cathode, and an anode, a connectionbetween said anode and cathode including a capacitive load device, aconnection between said control electrode and cathode including anoscillatory input circuit, said connections including a common conductorextending to said cathode, said common conductor having sufficientlength to produce feedback resulting in undesired damping of saidoscillatory circuit, and an inductance connected between said anode anda point intermediate of the length of said common conductor, said pointbeing chosen to reduce said damping.

6. The combination, in an electron discharge radio frequency amplifierhaving a control elec trode, a cathode, and an anode, a connectionbetween said anode and cathode including a capacitive load device, aconnection between said control electrode and cathode including a sourceof radio frequency electromotive force to be amplified, said connectionsincluding a common conductor extending to said cathode, said commonconductor having length sufficient toproduce undesired feedback fromsaid anode to said controlelectrode, and an inductance connected betweensaid anode and a point intermediate of the length of said commonconductor such that substantially zero voltage exists between the endsof said common conductor.

GEORGE W. FYLER.

on said first inductance of such value that said- CERTIFICATE OFCORRECTION. Patent No. 2,555,050. November 25, 191;}.

GEORGE W. FYLER.

It is hereby certified that error appears in the printed specificationof the above numbered patent requiring correction as follows: Page 2',second colum n, line 19, claim 3, for "contacted" read --connected--;and that the said Letters Patent should. be read with this correctiontherein that the same may" conform to the record of the case in thePatent Office Signed and sealed. this 25th day of January, A. D. 191m.

Henry Van Arsdale, (Seal) Acting Commissioner of Patents.

